The behavior of power amplifiers (PAs) driven by concurrent dual-band signals is analyzed theoretically in this paper. According to the analysis, the impedance matching at intermodulation (IM) frequency is very important for PAs working in concurrent mode. Based on the concept of IM impedance tuning, a family of new operation modes can be introduced, including concurrent Class-A, Class-AB, Class-B, and Class-C. The theoretical performance of these modes are derived and the overdrive effects of them are also discussed. A possible structure is proposed to implement the proposed IM impedance tuning, and a concurrent Class-AB dual-band example PA operating at 1.9-2.6-GHz long-term evolution (LTE) bands is demonstrated. Experimental results show good consistence with the theoretical analysis, and the concurrent Class-AB PA prototype exhibits higher than 36.1% power-added efficiency in concurrent mode when driven by 10- and 15-MHz LTE signals in two bands concurrently. To our best knowledge, this is the state-of-the-art efficiency performance of concurrent dual-band PAs, even higher than previously reported dual-band Doherty PAs. Additionally the proposed PA, which is fabricated using a 10-W GaN HEMT, can output more than 34.3-dBm power with a peak-to-average ratio of 7 dB in concurrent mode, showing a remarkable power utilization factor for concurrent dual-band PAs.